Current Status of Keratinized Matrices in Toxicology: Comparison of Hair and Nails

Nails are being explored as an alternative to hair for evaluating long-term drug use, but differences in structure, growth, and drug incorporation between nails and hair can complicate analysis and interpretation. This review compiles literature comparing drug concentrations in hair, fingernails, and toenails, emphasizing studies with paired samples from the same individuals. While some drugs show clear results, more standardized studies are necessary to fully understand drug incorporation in nails and establish reliable cut-offs.